Just want to check workflow with the experts

I'm running Yosemite on a 2010 Mac Pro with 2x2.93 GHz 6 core Xeon, with 64 GB ddr3 on Avid MC 8.

I'm editing MK3 footage so first I Mpegstreamclip the .MOV to .mov but DNxHD 175 8 bit with RGB color, alpha none.

I create a project in Avid with same settings but with 601 SD or 709 HD checked and Do not invert in the Alpha channel.

Is this correct? Despite the "fast import" it's not that fast lol - granted my clips are ~10 minutes each.

Also I'm experiencing lag during playback.

This is the first time using MC8, I used 6/7 extensively with this same computer no lag/problems at all.  

Thanks!